Method and apparatus for providing precise control of magnetic coupling field in NiMn top spin valve heads and amplitude enhancement

ABSTRACT

A method and apparatus for providing precise control of magnetic coupling field in NiMn top spin valve heads and amplitude enhancement is disclosed. The magnetic coupling between free and pinned layers in NiMn top spin valve heads is precisely controlled by employing the surface oxidation of Cu seed layer or/and Cu spacer layer that improve both the interfacial quality and the crystalline texture. According to the present invention the magnitude of coupling field can be precisely controlled without affecting resistance, and the amplitude of giant magneto-resistive(GMR) heads is improved by 15% at the same coupling field without affecting asymmetry performance. Thus, the present invention improves not only the interfacial roughness, but also improves the magnetic layer texture. The oxidation of Cu seed layer in the NiMn top spin valve structure provides more robust process with good control in coupling field that affects asymmetry of a GMR head.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates in general to spin valve heads formagnetic storage systems, and more particularly to a method andapparatus for providing precise control of magnetic coupling field inNiMn top spin valve heads and amplitude enhancement.

[0003] 2. Description of Related Art

[0004] Magnetic recording is a key and invaluable segment of theinformation-processing industry. While the basic principles are onehundred years old for early tape devices, and over forty years old formagnetic hard disk drives, an influx of technical innovations continuesto extend the storage capacity and performance of magnetic recordingproducts. For hard disk drives, the areal density or density of writtendata bits on the magnetic medium has increased by a factor of more thantwo million since the first disk drive was applied to data storage.Since 1991, areal density has grown by the well-known 60% compoundgrowth rate, and this is based on corresponding improvements in heads,media, drive electronics, and mechanics.

[0005] Magnetic recording heads have been considered the mostsignificant factor in areal-density growth. The ability of thesecomponents to both write and subsequently read magnetically recordeddata from the medium at data densities well into the Gbits/in² rangegives hard disk drives the power to remain the dominant storage devicefor many years to come.

[0006] The heart of a computer is an assembly that is referred to as amagnetic disk drive. The disk drive includes a rotating magnetic disk,write and read heads that are suspended by a suspension arm above therotating disk and an actuator that swings the suspension arm to placethe read and write heads over selected circular tracks on the rotatingdisk. The read and write heads are directly mounted on a slider that hasan air-bearing surface (ABS). The suspension arm biases the slider intocontact with the surface of the disk when the disk is not rotating.However, when the disk rotates, air is swirled by the rotating diskadjacent the ABS causing the slider to ride on an air bearing a slightdistance from the surface of the rotating disk. The write and read headsare employed for writing magnetic impressions to and reading magneticimpressions from the rotating disk. The read and write heads areconnected to processing circuitry that operates according to a computerprogram to implement the writing and reading functions.

[0007] A magnetoresistive (MR) sensor detects magnetic field signalsthrough the resistance changes of a sensing element, fabricated of amagnetic material, as a function of the strength and direction ofmagnetic flux being sensed by the sensing element. Conventional MRsensors, such as those used as a MR read heads for reading data inmagnetic recording disk drives, operate on the basis of the anisotropicmagnetoresistive (AMR) effect of the bulk magnetic material, which istypically permalloy (Ni₈₁Fe₁₉). A component of the read elementresistance varies as the square of the cosine of the angle between themagnetization direction in the read element and the direction of sensecurrent through the read element. Recorded data can be read from amagnetic medium, such as the disk in a disk drive, because the externalmagnetic field from the recorded magnetic medium (the signal field)causes a change in the direction of magnetization in the read element,which in turn causes a change in resistance of the read element and acorresponding change in the sensed current or voltage.

[0008] In the past several years, prospects of even more rapidperformance improvements have been made possible by the discovery anddevelopment of sensors based on the giant magnetoresistance (GMR)effect, also known as the spin-valve effect. Magnetic sensors utilizingthe GMR effect, frequently referred to as “spin valve” sensors,typically involve a sandwiched structure consisting of two ferromagneticlayers separated by a thin non-ferromagnetic layer. One of theferromagnetic layers is called the “pinned layer” because it ismagnetically pinned or oriented in a fixed and unchanging direction byan adjacent anti-ferromagnetic layer, commonly referred to as the“pinning layer,” through anti-ferromagnetic exchange coupling. The otherferromagnetic layer is called the “free” or “unpinned” layer because themagnetization is allowed to rotate in response to the presence ofexternal magnetic fields.

[0009] The benefits of spin valve sensors result from the large changeof conductance exhibited by the devices, which depends on the relativealignment between the magnetizations of the two ferromagnetic layers. Inorder to function effectively, a sufficient pinning field from thepinning layer is required to keep the pinned ferromagnetic layer'smagnetization unchanged during operation of the GMR sensor. Thus far,various anti-ferromagnetic materials, such as FeMn, NiO, IrMn, PtPdMn,and TbCo, have been used as pinning layers for spin valve sensors.However, these materials have provided less than desirable results. Forexample, for FeMn pinning layers, the temperature (referred to as theblocking temperature) at which the pinning field disappears (or isgreatly reduced) is very close to the typical sensor operatingtemperature of 100° C.-150° C. Therefore, at normal operatingtemperatures, an FeMn pinning layer typically does not provide a pinningfield of sufficient strength to prevent the magnetization of the pinnedferromagnetic layer from rotating in the presence of an externalmagnetic field. Without sufficient pinning strength, the spin valvecannot function to its full potential. Further, materials such as FeMnand TbCo are susceptible to corrosion. Also, oxide materials such asNiO, which provide a low pinning field as well, are difficult toprocess. IrMn and PtPdMn are both expensive materials which providepinning field strengths which are lower than is desired at normaloperating temperatures.

[0010] NiMn has properties which make it desirable for use as anexchange bias layer material to stabilize magnetic sensors. See forexample, Lin et al., “Improved Exchange Coupling Between FerromagneticNi—Fe and Antiferromagnetic Ni—Mn-based Films,” Appl. Phys. Lett., Vol.65, No. 9, pp. 1183-1185, Aug. 29, 1994. See also, Lin et al., U.S. Pat.No. 5,315,468 entitled “Magnetoresistive Sensor Having AntiferromagneticLayer for Exchange Bias.” These references discuss the use of NiMn as anexchange bias layer material to stabilize the MR sensor layer. However,the exchange fields must be kept low to avoid pinning the sensor layer,which would drastically reduce its sensitivity. NiMn is capable ofproviding high exchange fields at temperatures far in excess of thepinning layer materials mentioned above. In addition to its ability toprovide thermally stable exchange fields of high magnitude, NiMn is verycorrosion-resistant. As taught by Lin et al., a NiMn layer having athickness of around 500 Å can be used as an exchange bias layer adjacentto the MR sensor layer in a conventional MR sensor. However, thethickness and structure required for the MR sensor of Lin et al. are notcompatible with necessary spin valve sensor thickness and structures.

[0011] A problem with using NiMn as a pinning layer material in a spinvalve sensor is that, as is well-known in the art, heating a spin valvesensor to temperatures greater than 225°-240° C. for more than 2-3 hourshas resulted in inter-diffusion of the various layers and thus indestruction of the sensor. However, high annealing temperatures arenecessary in order to realize the high pinning fields desired from theNiMn. The inter-diffusion between the layers during high temperatureannealing has been an obstacle to using NiMn as a pinning layer in spinvalve sensors. See for example, Devasahayam et al., “Exchange Biasingwith NiMn,” DSSC Spring '96 Review, Carnegie Mellon University.

[0012] Attempts in the prior art to create a spin valve sensor havingNiMn as a pinning layer have failed. For example, Devasahayam et al.describe one such failed attempt in which the NiMn pinning layer ispre-annealed prior to depositing the NiFe ferromagnetic layer of thespin valve sensor. Devasahayam et al. describe another attempt to useNiMn as a pinning layer material in a spin valve sensor in which abi-layer of NiMn and NiFe are pre-annealed. Next, the layer of NiFe issputter etched away, and a new NiFe ferromagnetic layer is deposited ontop of the NiMn pinning layer. While some success was reported in thissecond attempted method, the device reported by Devasahayam et al.requires a NiFe ferromagnetic layer thickness of 250 Å and a NiMnpinning layer thickness of 500 Å, while achieving a pinning field ofonly 100 Oe.

[0013] Thus, in addition to providing insufficient pinning strengths,the thicknesses of the layers required by Devasahayam et al. areincompatible with spin valve sensor requirements. Further, the processof annealing and sputter etching the layer of NiFe and redepositing thelayer of NiFe is not practical for use in producing spin valve sensors.Therefore, there is a need for a spin valve sensor with thermally stablehigh pinning fields.

[0014] Spin valve sensors have been developed that include a first layerof ferromagnetic material and a second layer of ferromagnetic material,with the second layer of ferromagnetic material having a thickness ofless than about 100 Å. A first layer of non-ferromagnetic conductingmaterial is positioned between the first and second layers offerromagnetic material. A NiMn pinning layer is positioned adjacent tothe second layer of ferromagnetic material such that the pinning layeris in contact with the second layer of ferromagnetic material, whereinthe NiMn pinning layer has a thickness of less than about 200 Å andprovides a pinning field for pinning a magnetization of the second layerof ferromagnetic material in a first direction.

[0015] However, In such NiMn top spin valve heads, the Cu seed layerprior to deposition of magnetic free layers plays an important role inaffecting the magnetic coupling field and amplitude. With increasing Cuseed layer thickness, the ferromagnetic coupling field decreases sharplyand stays constant at 13 Å of Cu thickness, while the GMR effectincreases up to 20 Å of Cu thickness due to spin filtering effect.Typically the ferromagnetic coupling field of NiMn spin valve heads with15 Å thick Cu seed layer is 8-10 Oe and is difficult to be adjustedunless the Cu spacer thickness is changed. The precise control ofmagnetic coupling field is important in yielding high performance heads,since the coupling field sensitively affects the head performance suchas asymmetry, amplitude and asymmetry uniformity within the wafer.Besides, it is difficult to fabricate the head having a negativecoupling field using a NiMn spin valve structure because ofinterdiffusion of free and pinned layers during high temperatureannealing process (e.g., ˜250° C.)

[0016] It can be seen that there is a need for a method and apparatusfor providing precise control of magnetic coupling field in NiMn topspin valve heads and amplitude enhancement.

SUMMARY OF THE INVENTION

[0017] To overcome the limitations in the prior art described above, andto overcome other limitations that will become apparent upon reading andunderstanding the present specification, the present invention disclosesa method and apparatus for providing precise control of magneticcoupling field in NiMn top spin valve heads and amplitude enhancement.

[0018] The present invention solves the above-described problems byprecisely controlling the magnetic coupling between free and pinnedlayers in NiMn top spin valve heads by employing the surface oxidationof Cu seed layer or/and Cu spacer layer that improve both theinterfacial quality and the crystalline texture. According to thepresent invention the magnitude of coupling field can be preciselycontrolled without affecting resistance, and the amplitude of giantmagneto-resistive(GMR) heads is improved by 15% at the same couplingfield, i.e., asymmetry performance.

[0019] A method in accordance with the principles of the presentinvention includes forming at least one copper layer in a NiMn top spinvalve, oxidizing the at least one copper layer and depositing remaininglayers of the NiMn top spin valve head.

[0020] Other embodiments of a method in accordance with the principlesof the invention may include alternative or optional additional aspects.One such aspect of the method of the present invention is that the atleast one copper layer is naturally oxidized for 80 seconds under 8×10-5Torr of oxygen pressure.

[0021] Another aspect of the method of the present invention is that theat least one oxidized copper layer reduces the ferromagnetic couplingfield without deteriorating GMR effect or resistance.

[0022] Another aspect of the method of the present invention is that theat least one oxidized copper layer provides a negative coupling fieldwithout affecting GMR effect or resistance.

[0023] Another aspect of the present invention is that the at least oneoxidized copper layer changes the crystalline texture growth ofsubsequent magnetic layers.

[0024] Another aspect of the method of the present invention is that atleast one oxidized copper layer provides a negative coupling field thatis achieved without affecting a GMR effect or resistance of the NiMn topspin valve head.

[0025] Another aspect of the method of the present invention is that theat least one oxidized copper layer provides stronger growth of NiFe(111)and NiMn(111) with respect to NiFe(200) and NiMn(002) phases.

[0026] Another aspect of the method of the present invention is that theat least one oxidized copper layer improves the interfacial roughness.

[0027] Another aspect of the method of the present invention is that theat least one copper layer is oxidized prior to deposition of magneticfree layers.

[0028] Another aspect of the method of the present invention is that theat least one oxidized copper layer comprises a copper seed layer.

[0029] Another aspect of the method of the present invention is that theat least one oxidized copper layer further comprises a copper spacerlayer.

[0030] Another aspect of the method of the present invention is that theoxidation of at least one copper layer provides an approximately 15%increase in amplitude of the output of a NiMn spin valve head at thesame coupling field.

[0031] Another aspect of the method of the present invention is that theoxidation of at least one copper layer does not affect asymmetryperformance.

[0032] In another embodiment of the present invention, a NiMn top spinvalve sensor is disclosed. The NiMn top spin valve sensor includes asubstrate, a copper seed layer structure disposed on the substrate, aferromagnetic free layer having a magnetic moment that is free to rotatefrom a first direction in response to a signal field, a ferromagneticpinned layer structure having a magnetic moment, a nonmagneticelectrically conductive spacer layer of copper located between the freelayer and the pinned layer structure and a NiMn antiferromagneticpinning layer exchange coupled to the pinned layer structure for pinningthe magnetic moment of the pinned layer structure in a second direction,wherein at least one of the copper seed layer and the nonmagneticelectrically conductive spacer layer of copper is oxidized afterdeposition and before a subsequent layer is disposed thereon.

[0033] Another aspect of the NiMn top spin valve sensor according to thepresent invention is that at least one of the copper seed layer and thenonmagnetic electrically conductive spacer layer of copper is naturallyoxidized for 80 seconds under 8×10-5 Torr of oxygen pressure.

[0034] Another aspect of the NiMn top spin valve sensor according to thepresent invention is that both the copper seed layer and the nonmagneticelectrically conductive spacer layer of copper are oxidized afterdeposition and before a subsequent layer is deposited thereon.

[0035] Another aspect of the NiMn top spin valve sensor according to thepresent invention is that oxidation of at least one of the copper seedlayer and the nonmagnetic electrically conductive spacer layer of copperreduces the ferromagnetic coupling field without deteriorating GMReffect or resistance.

[0036] Another aspect of the NiMn top spin valve sensor according to thepresent invention is that oxidation of at least one of the copper seedlayer and the nonmagnetic electrically conductive spacer layer of copperprovides a negative coupling field without affecting GMR effect orresistance.

[0037] Another aspect of the NiMn top spin valve sensor according to thepresent invention is that oxidation of at least one of the copper seedlayer and the nonmagnetic electrically conductive spacer layer of copperchanges the crystalline texture growth of subsequent magnetic layers.

[0038] Another aspect of the NiMn top spin valve sensor according to thepresent invention is that oxidation of at least one of the copper seedlayer and the nonmagnetic electrically conductive spacer layer of copperresults in stronger growth of NiFe(111) and NiMn(111) with respect toNiFe(200) and NiMn(002) phases.

[0039] Another aspect of the NiMn top spin valve sensor according to thepresent invention is that oxidation of at least one of the copper seedlayer and the nonmagnetic electrically conductive spacer layer of copperimproves the interfacial roughness.

[0040] Another aspect of the NiMn top spin valve sensor according to thepresent invention is that oxidation of at least one of the copper seedlayer and the nonmagnetic electrically conductive spacer layer of copperprovides an approximately 15% increase in amplitude of the output of aNiMn spin valve head at the same coupling field.

[0041] Another aspect of the NiMn top spin valve sensor according to thepresent invention is that oxidation of at least one of the copper seedlayer and the nonmagnetic electrically conductive spacer layer of copperdoes not affect asymmetry performance.

[0042] Another aspect of the NiMn top spin valve sensor according to thepresent invention is that the at least one oxidized copper layer reducesthe ferromagnetic coupling field without deteriorating GMR effect orresistance.

[0043] In another embodiment of the present invention, a magneticstorage system is disclosed. The magnetic storage system includes amagnetic recording medium, a NiMn top spin valve sensor disposedproximate the recording medium, an actuator for moving the NiMn top spinvalve sensor across the magnetic recording medium so the NiMn top spinvalve sensor may access different regions of magnetically recorded dataon the magnetic recording medium and a data channel coupled electricallyto the NiMn top spin valve sensor for detecting changes in resistance ofthe NiMn top spin valve sensor caused by rotation of the magnetizationaxis of the free ferromagnetic layer relative to the fixed magnetizationof the pinned layer in response to magnetic fields from the magneticallyrecorded data, the NiMn top spin valve sensor including a substrate, acopper seed layer structure disposed on the substrate, a ferromagneticfree layer having a magnetic moment that is free to rotate from a firstdirection in response to a signal field, a ferromagnetic pinned layerstructure having a magnetic moment, a nonmagnetic electricallyconductive spacer layer of copper located between the free layer and thepinned layer structure and a NiMn antiferromagnetic pinning layerexchange coupled to the pinned layer structure for pinning the magneticmoment of the pinned layer structure in a second direction, wherein atleast one of the copper seed layer and the nonmagnetic electricallyconductive spacer layer of copper is oxidized after deposition andbefore a subsequent layer is disposed thereon, Another aspect of themagnetic storage system of the present invention is that at least one ofthe copper seed layer and the nonmagnetic electrically conductive spacerlayer of copper is naturally oxidized for 80 seconds under 8×10-5 Torrof oxygen pressure.

[0044] Another aspect of the magnetic storage system of the presentinvention is that both the copper seed layer and the nonmagneticelectrically conductive spacer layer of copper are oxidized afterdeposition and before a subsequent layer is disposed thereon.

[0045] Another aspect of the magnetic storage system of the presentinvention is that oxidation of at least one of the copper seed layer andthe nonmagnetic electrically conductive spacer layer of copper reducesthe ferromagnetic coupling field without deteriorating GMR effect orresistance.

[0046] Another aspect of the magnetic storage system of the presentinvention is that oxidation of at least one of the copper seed layer andthe nonmagnetic electrically conductive spacer layer of copper providesa negative coupling field without affecting GMR effect or resistance.

[0047] Another aspect of the magnetic storage system of the presentinvention is that oxidation of at least one of the copper seed layer andthe nonmagnetic electrically conductive spacer layer of copper changesthe crystalline texture growth of subsequent magnetic layers.

[0048] Another aspect of the magnetic storage system of the presentinvention is that oxidation of at least one of the copper seed layer andthe nonmagnetic electrically conductive spacer layer of copper resultsin stronger growth of NiFe(111) and NiMn(111) with respect to NiFe(200)and NiMn(002) phases.

[0049] Another aspect of the magnetic storage system of the presentinvention is that oxidation of at least one of the copper seed layer andthe nonmagnetic electrically conductive spacer layer of copper improvesthe interfacial roughness.

[0050] Another aspect of the magnetic storage system of the presentinvention is that oxidation of at least one of the copper seed layer andthe nonmagnetic electrically conductive spacer layer of copper providesan approximately 15% increase in amplitude of the output of a NiMn spinvalve head at the same coupling field.

[0051] Another aspect of the magnetic storage system of the presentinvention is that oxidation of at least one of the copper seed layer andthe nonmagnetic electrically conductive spacer layer of copper does notaffect asymmetry performance.

[0052] Another aspect of the magnetic storage system of the presentinvention is that the at least one oxidized copper layer reduces theferromagnetic coupling field without deteriorating GMR effect orresistance.

[0053] These and various other advantages and features of novelty whichcharacterize the invention are pointed out with particularity in theclaims annexed hereto and form a part hereof. However, for a betterunderstanding of the invention, its advantages, and the objects obtainedby its use, reference should be made to the drawings which form afurther part hereof, and to accompanying descriptive matter, in whichthere are illustrated and described specific examples of an apparatus inaccordance with the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Referring now to the drawings in which like reference numbersrepresent corresponding parts throughout:

[0055]FIG. 1 illustrates a storage system according to the presentinvention;

[0056]FIG. 2 illustrates one particular embodiment of a storage systemaccording to the present invention;

[0057]FIG. 3 illustrates a slider mounted on a suspension;

[0058]FIG. 4 is an ABS view of the slider and the magnetic head;

[0059]FIG. 5 is a cross-sectional schematic view of the integratedread/write head which includes a MR read head portion and an inductivewrite head portion;

[0060]FIG. 6 is a diagrammatic view illustrating one embodiment of aspin valve sensor stack having a pinning layer comprisingnickel-manganese;

[0061]FIG. 7 is a table showing the effect of the surface oxidation ofthe copper layers according to the present invention;

[0062]FIG. 8 illustrates the change of the coupling field with Cu spacerthickness;

[0063]FIG. 9 illustrates the magneto-resistive effect, dR (Ohm/sq), ofall types of GMR films as a function of Cu spacer thickness;

[0064]FIG. 10 shows the free-to-pinned layer coupling field versusin-situ Cu surface oxidation of the Cu seed layer;

[0065]FIG. 11 shows the free-to-pinned layer coupling field versusin-situ Cu surface oxidation of the Cu spacer layer; and

[0066]FIG. 12 illustrates a method for providing precise control ofmagnetic coupling field in NiMn top spin valve heads according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

[0067] In the following description of the exemplary embodiment,reference is made to the accompanying drawings which form a part hereof,and in which is shown by way of illustration the specific embodiment inwhich the invention may be practiced. It is to be understood that otherembodiments may be utilized as structural changes may be made withoutdeparting from the scope of the present invention.

[0068] The present invention provides a method and apparatus forproviding precise control of magnetic coupling field in NiMn top spinvalve heads and amplitude enhancement. The present invention solves theabove-described problems by precisely controlling the magnetic couplingbetween free and pinned layers in NiMn top spin valve heads by employingthe surface oxidation of Cu seed layer or/and Cu spacer layer thatimprove both the interfacial quality and the crystalline texture.According to the present invention the magnitude of coupling field canbe precisely controlled without affecting resistance, and the amplitudeof giant magneto-resistive(GMR) heads is improved by 15% at the samecoupling field or asymmetry value. Thus, the present invention improvesnot only the interfacial roughness, but also improves the magnetic layertexture. The oxidation of Cu seed layer in the NiMn top spin valvestructure provides more robust process with good control in couplingfield.

[0069]FIG. 1 illustrates a storage system 100 according to the presentinvention. In FIG. 1, a transducer 110 is under control of an actuator120. The actuator 120 controls the position of the transducer 110. Thetransducer 110 writes and reads data on magnetic media 130. Theread/write signals are passed to a data channel 140. A system processor150 controls the actuator 120 and processes the signals of the datachannel 140. In addition, a media translator 160 is controlled by asystem processor 150 to cause the magnetic media 130 to move relative tothe transducer 110. The present invention is not meant to be limited toa particular type of storage system 100 or to the type of media 130 usedin the storage system 100.

[0070]FIG. 2 illustrates one particular embodiment of a storage system200 according to the present invention. In FIG. 2, a hard disk drive 200is shown. The drive 200 includes a spindle 210 that supports and rotatesa magnetic disk 214. The spindle 210 is rotated by a motor 220 that iscontrolled by a motor controller 230. A combined read and write magnetichead 240 is mounted on a slider 242 that is supported by a suspension244 and actuator arm 246. Processing circuitry 250 exchanges signals,representing such information, with the head 240, provides motor drivesignals for rotating the magnetic disk 214, and provides control signalsfor moving the slider to various tracks. A plurality of disks 214,sliders 242 and suspensions 244 may be employed in a large capacitydirect access storage device (DASD).

[0071] The suspension 244 and actuator arm 246 position the slider 242so that the magnetic head 240 is in a transducing relationship with asurface of the magnetic disk 214. When the disk 214 is rotated by themotor 220 the slider 240 is supported on a thin cushion of air (airbearing) between the surface of the disk 214 and the air-bearing surface(ABS) 248. The magnetic head 240 may then be employed for writinginformation to multiple circular tracks on the surface of the disk 214,as well as for reading information therefrom.

[0072]FIG. 3 illustrates a slider 310 mounted on a suspension 312. InFIG. 3 first and second solder connections 304 and 306 connect leadsfrom the sensor 308 to leads 313 and 314 on the suspension 312 and thirdand fourth solder connections 316 and 318 connect the coil 384 to leads324 and 326 on the suspension.

[0073]FIG. 4 is an ABS view of the slider 400 and the magnetic head 404.The slider has a center rail 456 that supports the magnetic head 404,and side rails 458 and 460. The rails 456, 458 and 460 extend from across rail 462. With respect to rotation of a magnetic disk, the crossrail 462 is at a leading edge 464 of the slider and the magnetic head404 is at a trailing edge 466 of the slider.

[0074]FIG. 5 is a cross-sectional schematic view of the integratedread/write head 525 which includes a MR read head portion and aninductive write head portion. The head 525 is lapped to form anair-bearing surface (ABS), the ABS being spaced from the surface of therotating disk by the air bearing as discussed above. The read headincludes a MR sensor 540 sandwiched between first and second gap layersG1 and G2 which are, in turn, sandwiched between first and secondmagnetic shield layers S1 and S2. In a conventional disk drive, the MRsensor 540 is an AMR sensor. The write head includes a coil layer C andinsulation layer 512 which are sandwiched between insulation layers 511and 513 which are, in turn, sandwiched between first and second polepieces P1 and P2. A gap layer G3 is sandwiched between the first andsecond pole pieces P1, P2 at their pole tips adjacent to the ABS forproviding a magnetic gap. During writing, signal current is conductedthrough the coil layer C and flux is induced into the first and secondpole layers P1, P2 causing flux to fringe across the pole tips at theABS. This flux magnetizes circular tracks on the rotating disk during awrite operation. During a read operation, magnetized regions on therotating disk inject flux into the MR sensor 540 of the read head,causing resistance changes in the MR sensor 540. These resistancechanges are detected by detecting voltage changes across the MR sensor540. The combined head 525 shown in FIG. 5 is a “merged” head in whichthe second shield layer S2 of the read head is employed as a first polepiece P1 for the write head. In a piggyback head (not shown), the secondshield layer S2 and the first pole piece P1 are separate layers.

[0075] The above description of a typical magnetic recording disk drivewith an AMR read head, and the accompanying FIGS. 1-5, are forrepresentation purposes only. Disk drives may contain a large number ofdisks and actuators, and each actuator may support a number of sliders.In addition, instead of an air-bearing slider, the head carrier may beone which maintains the head in contact or near contact with the disk,such as in liquid bearing and other contact and near-contact recordingdisk drives.

[0076] As mentioned above, NiMn has properties which make it desirablefor use as an exchange bias layer material to stabilize magneticsensors. In such NiMn top spin valve heads, an appropriatecrystallographic texture of seed and underlayers prior to deposition ofmagnetic free, pinned and pinning NiMn layers are critical indetermining coupling field as well as NiMn pinning field. According tothe present invention, the NiMn top spin valve heads includes copperseed layers for enhancing GMR amplitude through spin filtering effect.

[0077]FIG. 6 is a diagrammatic view illustrating one embodiment of aspin valve sensor stack 600 having a pinning layer comprisingnickel-manganese. The spin valve sensors illustrated in the FIG. 6represent only the spin valve sensor stack. Other layers and featuresmay be added to the spin valve sensor stacks as desired. Spin valvesensor 600 includes substrate 612, oxidized copper (Cu) seed layer 614,unpinned or free ferromagnetic layer 619, which may include a layer ofNiFe and CoFe, non-ferromagnetic copper layer 620, a second oxidizedcopper layer 622, pinned ferromagnetic layer 625, NiMn pinning layer 626and cap layer 628.

[0078] NiMn pinning layer 626 may have a composition of between about 45and 55 atomic percent Mn and a thickness of between about 80 Å and 200Å. Cap layer 628 preferably, but not exclusively, includes a thicknessof approximately 80 Å. Cap layer 628 maintains the integrity of thestructure during subsequent processing.

[0079] However, as also described earlier, with increasing Cu seed layerthickness, the ferromagnetic coupling field decreases sharply and staysconstant, while the GMR effect increases due to spin filtering effect.Typically the ferromagnetic coupling field of NiMn spin valve heads isdifficult to be adjusted unless the Cu spacer thickness is changed. Theprecise control of magnetic coupling field is important in yielding highperformance heads, since the coupling field sensitively affects the headperformance such as asymmetry, amplitude and asymmetry uniformity withinthe wafer.

[0080] As the magnetic free layer 619 gets thinner, its thermalstability gets worse by diffusion of adjacent layer atoms into the freelayer 619 and the magnetic thickness decreases by an increased ratio ofmagnetic dead layer to physical thickness. In particular, magneticanisotropy or the magnetostriction of the free layer 619 is stronglydependent on thickness, type of neighboring atoms and annealtemperature. See for example, Geon Choe “Giant interfacemagnetostriction and temperature dependence in NiFe films encapsulatedwith Ta and Al203 layers,” IEEE Trans. Magn. Vol.35(5), p3838, 1999. Fora very thin free layer 619, effective magnetostriction is given byλ_(eff)=λ_(b)+λ_(i)/(t−t₀)where, λ_(b) is bulk magnetostriction, λ_(i)is interfacial magnetostriction, t is film thickness and t_(o) ismagnetic dead layer thickness. Thus, the mangnetostriction in GMR headsplays an important role in influencing the output sensitivity of thehead, the stability and the optimum bias point.

[0081] As the GMR sensor layer thickness becomes thinner with increasingareal density, control of magnetostriction becomes more difficult due tothe combination of giant interfacial magnetostriction dominating overbulk magnetostriction in the thinner free layer 619 and the potentiallylarger stress concentrated in shorter GMR stripes. Thus, according tothe present invention, the copper seed 614 and spacer 622 layers areoxidized. The present invention therefore provides interfacialmagnetostriction of free layer that is thermally more stable than thecase without oxidation.

[0082]FIG. 7 is a table showing the effect of the surface oxidation ofthe copper layers according to the present invention. FIG. 7 shows theinterfacial magnetostriction and bulk magnetostriction for the depositedfree layer and the annealed free layer at, for example, 250° C. for 5hours without oxidation and with copper seed layer and spacer layeroxidation. FIG. 7 demonstrates the interfacial magnetostriction of freelayer being thermally more stable than the case without oxidation.Interfacial magnetostriction is strongly affected by interdiffusionbetween layers and determines the effective magnetostriction thataffects asymmetry of GMR head. By oxidizing the copper seed and spacerlayers according to the present invention, magnetostriction changes offree layer before and after annealing process can be significantlyreduced, indicating an enhanced thermal stability of magnetostrictionresulting in more stable GMR head whose asymmetry is less susceptible tothermal processing. Typically, it is difficult to fabricate NiMn spinvalve heads with a negative coupling field after high temperatureannealing processes because of the interdiffusion of free and pinnedlayers. However, the present invention may achieve a negative couplingfield without affecting GMR effect or resistance.

[0083]FIG. 8 is a plot 800 of the change of the coupling field 810 withCu spacer thickness 820. FIG. 8 shows the plot for an oxidized Cu seedlayer 830, a non-oxidized GMR film 832, an oxidized Cu spacer layer 833and oxidation of both Cu seed and spacer layers 834. The coupling fieldof GMR films with oxidized Cu seed layer 830 is decreased by 5 Oecompared to non-oxidized GMR films 832 over a wide range of Cu spacerthickness and the coupling field is more decreased with oxidation ofboth Cu seed and spacer layers 834.

[0084]FIG. 9 is a plot 900 of the magneto-resistive effect 910, dR(Ohm/sq), of all types of GMR films as a function of Cu spacer thickness920. Independent of oxidation treatment, the MR values of all the filmsfit into a linear line 930, indicating that oxidation does not affectthe spin polarization effect. From the slope of dR vs. Cu spacerthickness, more than 15% of amplitude increase is expected for NiMn spinvalve heads with the Cu seed and spacer layer oxidation method at thesame coupling field. Moreover, the amplitude increase may be achievedwithout affecting asymmetry performance.

[0085]FIGS. 10 and 11 show the free-to-pinned layer coupling fieldversus in-situ Cu surface oxidation of NiMn top spin valve films. InFIG. 10, the effect of oxidation of the Cu seed layer 1000 on H_(f)1010, R_(s) 1020 and GMR effect 1030 is shown for a wide oxidationprocess. FIG. 11, the effect of oxidation of the Cu spacer layer 1100 onH_(f) 1110, R_(s) 1120 and GMR effect 1130 is shown for a wide oxidationprocess.

[0086] Accordingly, the present invention provides a method forproviding precise control of magnetic coupling field in NiMn top spinvalve heads and amplitude enhancement. The present invention solves theabove-described problems with NiMn top spin valves by preciselycontrolling the magnetic coupling between free and pinned layers byemploying the surface oxidation of Cu seed layer or/and Cu spacer layerthat improve both the interfacial quality and the crystalline texture.

[0087]FIG. 12 illustrates a method 1200 for providing precise control ofmagnetic coupling field in NiMn top spin valve heads according to thepresent invention. Forming a Cu layer in a NiMn top spin valve 1210.After the Cu layer is formed, e.g. the Cu seed layer and/or Cu spacerlayer, it is oxidized 1220. Then subsequent layers are deposited 1230.In a preferred embodiment, a Cu layer is naturally oxidized for 80seconds under 8×10-5 Torr of oxygen pressure before the subsequentlayers were deposited.

[0088] The oxidation of the Cu layer reduces the ferromagnetic couplingfield without deteriorating GMR effect or resistance. The oxidized Cuseed layer changes the crystalline texture growth of subsequent magneticlayers, resulting in the stronger growth of NiFe(111) and NiMn(111) withrespect to NiFe(200) and NiMn(002) phases, while the oxidation of Cuspacer layer appears to improve the interfacial roughness.

[0089] The foregoing description of the exemplary embodiment of theinvention has been presented for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Many modifications andvariations are possible in light of the above teaching. It is intendedthat the scope of the invention be limited not with this detaileddescription, but rather by the claims appended hereto.

What is claimed is:
 1. A method for providing precise control ofmagnetic coupling field in NiMn top spin valve head, comprising: formingat least one copper layer in a NiMn top spin valve; oxidizing the atleast one copper layer; and depositing remaining layers of the NiMn topspin valve head.
 2. The method of claim 1 wherein the at least onecopper layer is naturally oxidized for 80 seconds under 8×10-5 Torr ofoxygen pressure.
 3. The method of claim 1 wherein the at least oneoxidized copper layer reduces the ferromagnetic coupling field withoutdeteriorating GMR effect or resistance.
 4. The method of claim 1 whereinthe at least one oxidized copper layer provides a negative couplingfield without affecting GMR effect or resistance.
 5. The method of claim1 wherein the at least one oxidized copper layer changes the crystallinetexture growth of subsequent magnetic layers.
 6. The method of claim 1wherein the at least one oxidized copper layer provides a negativecoupling field that is achieved without affecting a GMR effect orresistance of the NiMn top spin valve head.
 7. The method of claim 6wherein the at least one oxidized copper layer provides stronger growthof NiFe(111) and NiMn(111) with respect to NiFe(200) and NiMn(002)phases.
 8. The method of claim 1 wherein the at least one oxidizedcopper layer improves the interfacial roughness.
 9. The method of claim1 wherein the at least one copper layer is oxidized prior to depositionof magnetic free layers.
 10. The method of claim 1 wherein the at leastone oxidized copper layer comprises a copper seed layer.
 11. The methodof claim 10 wherein the at least one oxidized copper layer furthercomprises a copper spacer layer.
 12. The method of claim 1 wherein theoxidation of at least one copper layer provides an approximately 15%increase in amplitude of the output of a NiMn spin valve head at thesame coupling field.
 13. The method of claim 12 wherein the oxidation ofat least one copper layer does not affect asymmetry performance.
 14. Themethod of claim 1 wherein the at least one oxidized copper layercomprises a copper spacer layer.
 15. A NiMn top spin valve sensorcomprising: a substrate; a copper seed layer structure disposed on thesubstrate; a ferromagnetic free layer having a magnetic moment that isfree to rotate from a first direction in response to a signal field; aferromagnetic pinned layer structure having a magnetic moment; anonmagnetic electrically conductive spacer layer of copper locatedbetween the free layer and the pinned layer structure; and a NiMnantiferromagnetic pinning layer exchange coupled to the pinned layerstructure for pinning the magnetic moment of the pinned layer structurein a second direction; wherein at least one of the copper seed layer andthe nonmagnetic electrically conductive spacer layer of copper isoxidized after deposition and before a subsequent layer is disposedthereon.
 16. The NiMn top spin valve sensor of claim 15 wherein at leastone of the copper seed layer and the nonmagnetic electrically conductivespacer layer of copper is naturally oxidized for 80 seconds under 8×10-5Torr of oxygen pressure.
 17. The NiMn top spin valve sensor of claim 15wherein both the copper seed layer and the nonmagnetic electricallyconductive spacer layer of copper are oxidized after deposition andbefore a subsequent layer is deposited thereon.
 18. The NiMn top spinvalve sensor of claim 17 wherein both the copper seed layer and thenonmagnetic electrically conductive spacer layer of copper are naturallyoxidized for 80 seconds under 8×10-5 Torr of oxygen pressure.
 19. TheNiMn top spin valve sensor of claim 15 wherein oxidation of at least oneof the copper seed layer and the nonmagnetic electrically conductivespacer layer of copper reduces the ferromagnetic coupling field withoutdeteriorating GMR effect or resistance.
 20. The NiMn top spin valvesensor of claim 15 wherein oxidation of at least one of the copper seedlayer and the nonmagnetic electrically conductive spacer layer of copperprovides a negative coupling field without affecting GMR effect orresistance.
 21. The NiMn top spin valve sensor of claim 15 whereinoxidation of at least one of the copper seed layer and the nonmagneticelectrically conductive spacer layer of copper changes the crystallinetexture growth of subsequent magnetic layers.
 22. The NiMn top spinvalve sensor of claim 21 wherein oxidation of at least one of the copperseed layer and the nonmagnetic electrically conductive spacer layer ofcopper results in stronger growth of NiFe(111) and NiMn(111) withrespect to NiFe(200) and NiMn(002) phases.
 23. The NiMn top spin valvesensor of claim 15 wherein oxidation of at least one of the copper seedlayer and the nonmagnetic electrically conductive spacer layer of copperimproves the interfacial roughness.
 24. The NiMn top spin valve sensorof claim 15 wherein oxidation of at least one of the copper seed layerand the nonmagnetic electrically conductive spacer layer of copperprovides an approximately 15% increase in amplitude of the output of aNiMn spin valve head at the same coupling field.
 25. The NiMn top spinvalve sensor of claim 24 wherein oxidation of at least one of the copperseed layer and the nonmagnetic electrically conductive spacer layer ofcopper does not affect asymmetry performance.
 26. The NiMn top spinvalve sensor of claim 15 wherein the at least one oxidized copper layerreduces the ferromagnetic coupling field without deteriorating GMReffect or resistance.
 27. A magnetic storage system, comprising: amagnetic recording medium; a NiMn top spin valve sensor disposedproximate the recording medium, the NiMn top spin valve sensor,comprising a substrate; a copper seed layer structure disposed on thesubstrate; a ferromagnetic free layer having a magnetic moment that isfree to rotate from a first direction in response to a signal field; aferromagnetic pinned layer structure having a magnetic moment; anonmagnetic electrically conductive spacer layer of copper locatedbetween the free layer and the pinned layer structure; and a NiMnantiferromagnetic pinning layer exchange coupled to the pinned layerstructure for pinning the magnetic moment of the pinned layer structurein a second direction; wherein at least one of the copper seed layer andthe nonmagnetic electrically conductive spacer layer of copper isoxidized after deposition and before a subsequent layer is disposedthereon an actuator for moving the NiMn top spin valve sensor across themagnetic recording medium so the NiMn top spin valve sensor may accessdifferent regions of magnetically recorded data on the magneticrecording medium; and a data channel coupled electrically to the NiMntop spin valve sensor for detecting changes in resistance of the NiMntop spin valve sensor caused by rotation of the magnetization axis ofthe free ferromagnetic layer relative to the fixed magnetization of thepinned layer in response to magnetic fields from the magneticallyrecorded data.
 28. The magnetic storage system of claim 27 wherein atleast one of the copper seed layer and the nonmagnetic electricallyconductive spacer layer of copper is naturally oxidized for 80 secondsunder 8×10-5 Torr of oxygen pressure.
 29. The magnetic storage system ofclaim 27 wherein both the copper seed layer and the nonmagneticelectrically conductive spacer layer of copper are oxidized afterdeposition and before a subsequent layer is disposed thereon.
 30. Themagnetic storage system of claim 29 wherein both the copper seed layerand the nonmagnetic electrically conductive spacer layer of copper arenaturally oxidized for 80 seconds under 8×10-5 Torr of oxygen pressure.31. The magnetic storage system of claim 27 wherein oxidation of atleast one of the copper seed layer and the nonmagnetic electricallyconductive spacer layer of copper reduces the ferromagnetic couplingfield without deteriorating GMR effect or resistance.
 32. The magneticstorage system of claim 27 wherein oxidation of at least one of thecopper seed layer and the nonmagnetic electrically conductive spacerlayer of copper provides a negative coupling field without affecting GMReffect or resistance.
 33. The magnetic storage system of claim 27wherein oxidation of at least one of the copper seed layer and thenonmagnetic electrically conductive spacer layer of copper changes thecrystalline texture growth of subsequent magnetic layers.
 34. Themagnetic storage system of claim 33 wherein oxidation of at least one ofthe copper seed layer and the nonmagnetic electrically conductive spacerlayer of copper results in stronger growth of NiFe(111) and NiMn(111)with respect to NiFe(200) and NiMn(002) phases.
 35. The magnetic storagesystem of claim 27 wherein oxidation of at least one of the copper seedlayer and the nonmagnetic electrically conductive spacer layer of copperimproves the interfacial roughness.
 36. The magnetic storage system ofclaim 27 wherein oxidation of at least one of the copper seed layer andthe nonmagnetic electrically conductive spacer layer of copper providesan approximately 15% increase in amplitude of the output of a NiMn spinvalve head at the same coupling field.
 37. The magnetic storage systemof claim 36 wherein oxidation of at least one of the copper seed layerand the nonmagnetic electrically conductive spacer layer of copper doesnot affect asymmetry performance.
 38. The magnetic storage system ofclaim 27 wherein the at least one oxidized copper layer reduces theferromagnetic coupling field without deteriorating GMR effect orresistance.